Celebrating the 1919 Eclipse at Principe

This special project will celebrate the historic 1919 eclipse expedition, led by Sir Arthur Eddington and organised by the Royal Astronomical Society, to the African equatorial island of Príncipe.

Historians now recognise the Principe expedition, together with the parallel expedition conducted to Sobral in Brazil, as a major achievement of 20th century science. By comparing the positions of stars in the Hyades star cluster at the time of the eclipse with those determined earlier, the gravitational deflection of 1.75 arcsec predicted by Albert Einstein's theory of relativity was satisfactorily verified. Today, Arthur Eddington can be considered one of the most distinguished British astronomers whose persistence and scientific conviction in pursuing the expedition were largely responsible for Einstein's fame (M. Stanley, Practical Mystic. Chicago 2007). Although neither Einstein nor Eddington foresaw any practical applications for gravitational lensing (the deflection of light rays by massive objects), ninety years later it has emerged as the most promising probe of our Universe.

The aim of the project is, by celebrating the expedition's 90th anniversary, to explain, for the benefit of the local population and international visitors, the historic significance and how gravitational lensing is shaping contemporary scientific understandings of the Universe. This will establish, on the one hand, local recognition of the importance of astronomy, particularly for young people. On the other hand, it will help preserve a site of significant cultural value and create an additional point of attraction beneficial to the emerging tourist industry and the population of São Tomé e Príncipe, now an independent island state.

For the occasion of the anniversary of the eclipse on 29 May 2009, we will in collaboration with the local government and population and with international institutional support:

- unveil an interpretative plaque in a ceremony at Sundy, the former plantation on Príncipe where the measurements were taken

- give lectures on the science and history underpinning the expedition both in Príncipe and in the capital of São Tomé, as well as in Lisbon, and

- install an illustrative exhibition of the progress made in gravitational lensing from 1919 to the present day in São Tomé.

Our activities will be accompanied and complemented by a local educational campaign carried out by the government of São Tomé e Príncipe and other national and international activities. More information can be found on our website: